Argon in JET Optimised Shear Plasmas

AND INTRODUCTION During the JET Mark IIGB campaign Argon radiation has been used to control the edge (resulting in type III ELMs or L-Mode edge) and to prolong the duration of op timised shear (OS) discharges with internal transport barriers (ITBs) (1,2). This results in weak barriers less prone to disruptions. The best discharges maintain quasi steady-state conditions for up to 3 energy confinement times with neutron yields up to equivalent Q DT≈0.4 at typical βN≈2. In these discharges Argon accumulates in the core region with typical dilution of nd/ne≅0.7 and Zeff on axis up to 4.5, with contributions from Argon of Δnd/ne≅-0.2 and ΔZeff≅3. There are indications that the Argon concentration would saturate at a higher level, if the discharges were further extended. Transport analysis shows that the accumulation is due to a strong inward convection in the ITB region, combined with a weak inward convection in the core.